Tomato Growers: Be On The Lookout

Purdue Report by Jeanne Gibson

After late blight was such a burden in 2009, Indiana tomato growers may be wondering if the disease will hit again this year.

Recent confirmations of late blight in Kentucky and Pennsylvania should make both commercial and homeowner tomato growers more cautious -- especially the Kentucky outbreak which is located in the northern part of the state between Indiana and Ohio, said Dan Egel, Purdue Extension plant pathologist.

“Late blight of tomato causes large brown lesions on tomato leaves and stems that under moist conditions are often ringed with the white fungus that causes the late blight,” Egel said. “Symptoms caused by late blight may look like other common tomato diseases and thus may be easily missed if not sent for accurate diagnosis.”

The plausible cause for late blight in 2009 is that it came from infected tomato transplants and was spread to other plants before it could be stopped. The disease infected plants in more than 39 Indiana counties last year.

Growers who suspect the disease can contact a county Extension educator and send a sample to the Purdue Plant and Pest Diagnostic Laboratory. For more information, visit the lab’s website at http://www.ppdl.purdue.edu/ppdl/

Fungicides containing the active ingredient chlorothalonil are available to homeowners and will help stop the spread of late blight and other diseases. Organic growers may find that copper products will slow the disease’s spread.

Commercial growers have many fungicide options and should refer to the Midwest Vegetable Production Guide for Commercial Growers (http://www.btny.purdue. edu/Pubs/ID/id-56/) and the Vegetable Crops hotline (http://www. btny.purdue.edu/pubs/vegcrop/ index2010.html) for recommendations and details.

More information about late blight is available through a Purdue University Extension fact sheet at http://www.extension.purdue. edu/extmedia/BP/BP-80-W.pdf or an Ohio State University Extension fact sheet at http://ohioline. osu.edu/hyg-fact/3000/3102.html.